The present invention concerns a method for making laminates, whereby under laminates is understood in particular layers of glass, plastic or other rigid materials which, either or not combined, are attached to one another by means of intermediate layers formed on the basis of a polymerizable mixture such as a resin or a glue.
In particular, the invention concerns a method which is mainly applied in the glass industry for the manufacturing of single- or multi-laminated glass which consists of at least two glass layers in between which is provided a layer of curable resin.
The laminated glass product obtained according to the invention can be used, depending on the resin used, for different purposes such as sound-insulating glass, bullet-proof glass, fire-retardant glass or such, and it can be combined with thermal insulating glass, with double glazing, mirrors, ornamental glass and such.
A known method for manufacturing laminated glass makes use of transparent PVB (polyvinylbutyral) film and/or PU (polyurethane) film and consists in that one or several of the above-mentioned films are provided between two glass plates, after which the whole is heated in an autoclave at a temperature of about 140 degrees Celsius for about three quarters of an hour and is pressed together so as to obtain a good bond and fuse of the films in relation to one another and in relation to both glass plates.
Although, according to this method, an excellent uniform layer thickness is obtained between the glass plates, it is disadvantageous in that the composition, heating and compression cannot be carried out as a continuous process, so that this method can never be implemented entirely automatically.
Another disadvantage is that this method is restricted by the specific characteristics of the PVB film or PU film itself, which implies that laminates with other or special characteristics cannot be realized.
Other known methods are based on placing two glass plates exactly parallel at a required distance, after which the space between these plates is filled with a liquid resin which is then chemically cured, or whereby the whole is exposed to ultraviolet light of a suitable wavelength, as a result of which the resin cures and also bonds to the glass surfaces.
Mostly, the space between the glass plates is filled with resin while the glass plates are placed vertically.
As the hydrostatic pressure of the liquid resin column in the almost vertical position on both glass plates increases towards the bottom, the lower parts of these glass plates tend to move outward, which inevitably leads to a non-uniform layer thickness of the resin. This may cause tension zones in the whole during and after the curing, which may lead to a delamination effect, i.e. the coming off of the cured resin layer on one or both glass plates.
GB 1 367 977 reveals in what manner the disadvantageous effect of the hydrostatic pressure of the liquid resin layer on the glass plates can be remedied by providing a hydrostatic counteracting pressure. To this end, the glass plates are placed vertically in a receiver, whereby this receiver is gradually filled with a liquid and whereby the layer of liquid, curable resin is simultaneously applied between the glass plates. The resin cures as the liquid in the receiver is heated.
An analogous method is described in CH 574 371, whereby the liquid is water.
These methods are time-consuming and cannot guarantee that the glass plates remain nicely parallel.
According to DE 22 26 342 and DE 26 06 569, the liquid, curable resin layer is inserted between the glass plates when they are vertically positioned, whereas the resin is cured between the glass plates when they are horizontally positioned.
The latter methods cannot guarantee that the bulging of the glass plates is entirely remedied as a result thereof, whereby an underpressure is applied in the resin layer according to DE 22 26 342 so as to avoid said bulging as much as possible.
According to GB 20 15 427, the space between the vertically positioned plates is filled with liquid, curable resin on the one hand, and the curing of this resin by means of the exposure to ultraviolet light on the other hand, is carried out step by step in successive layers so as to restrict the hydrostatic pressure in this manner.
The disadvantage of this method is that the curing of a first layer and the subsequent application of the next layer must take place uninterruptedly, since, if the first layer becomes too hard before the next layer is applied, this will result in a visible, very inconvenient horizontal dividing line between these layers.
In U.S. Pat. No. 4,828,784 is applied a similar method whereby an additional lateral pressure can be exerted by means of pressure rollers during the continuous filling and curing of the successive layers of moulding resin.
According to other known methods, a liquid curable resin layer is applied on a horizontally positioned lower glass plate, after which a top glass plate is applied, and whereby the liquid resin is subsequently cured by means of ultraviolet light of a suitable wave length.
An example of such a horizontal positioning is described in DE 27 28 762, but the problem of the bending of the top glass plate on the liquid resin and on the lower glass plate is not discussed.
Another example thereof is described in EP 200 394, in which the lower glass plate is bent such that it represents a concave central zone in which the curable resin is cast and after which a top glass plate is applied thereupon. Hereby, the edges of the laminate in preparation are sealed with tape, such that the thus obtained confinement remains permeable to air, whereas the resin is prevented from dripping out of the laminate in preparation. Subsequently, the lower glass plate is put in a flat, horizontal position, and pressure is then exerted on the top glass plate, so that the resin can spread evenly, whereby the entrapped air bubbles are laterally driven out of the resin at the same time.
U.S. Pat. No. 4,724,023 is based on the same method, whereby the tub shape of the lower glass plate is obtained thanks to a suction cup placed centrally under the glass plate onto which a weight is fixed.
These latter methods are disadvantageous in that the thickness of the resin layer is restricted by the maximal bending and the thus created cavity of the glass plate. Moreover, entrapped air bubbles are hard to avoid and remaining air bubbles are difficult to remove.
Another serious disadvantage is that the top layer, due to its own weight and due to the fact that the resin layer is applied in a liquid state, can bend through in the middle, so that a non-uniform layer thickness is obtained which may possibly result in a delamination of the resin layer.
A common characteristic of all the preceding and other methods making use of the above-mentioned filling processes is that the resin to be used must be sufficiently liquid, which implies that sufficiently high concentrations of monomers, which have a diluting effect on these resins, must be present in the composition. The content of monomers determines the viscosity of the composition which, for the resins used in the above-described methods, have a value situated between 7 and 300 mPa.sec.
A serious disadvantage thereof is that a high concentration of monomers in the liquid resin increases the inflammability and the toxic characteristics of these resins.
Another disadvantage related to the high concentration of monomers in the liquid resin is that, during the curing, the resin layer shrinks significantly, which may cause visible cracks and fissures in this layer, especially if the layer shrinks too fast.
U.S. Pat. No. 4,999,071 discloses a method whereby a glass plate is coated with a heat-polymerizable plastisol, and heated to polymerize partially this plastisol, after which another glass plate is laminated thereon and the laminate is heated to polymerize entirely the plastisol.